Variable condenser



July 19, 1949. w. M. TowLE VARIABLE CONDENSER 2 Sheets-Sheet l FiledAug. 19, 1946 July 19, W, M, TQWLE VARIABLE CONDENSER 2 Sheets-Sheet 2Filed Aug. 19, 194e Patented July 19, 1949 uit'Irun sn'ltrlss] PATENTortica' WillardxvM?. Towle,x Chicago, Ill., assigner. to Mid westLahoratories,.1nc., Chicago, I1I. a corporation ofllinois vAspplicatilLAlrg'ust I9, 19426, Serial N1?. 691,633

,myention relatesy to. improvements in. vari-- able-condensers..

It, one obiect. to provide a new type of. tarmble condenser` may.tk beused con'` nections with alt of. RF instruments, will' be cheap; easy;Vto: manufacture, compact, takeup little? neem im the: while giving`more` roomk wom where ismeeded, subject to3 exceiJ' tional?. otadjustxnent,A madel almost en'- tiselyricif. stamped' out ports andwherein, the condenser platesc be easily and conveniently shaped;rtiefgizvef any dcsiuelf tuning'. The con lpropone is; plaid-,l remainsin adjustment,v gives accusa-us tuning, may be I used ineconnectionwith: amuiinlietyf op arrangements of. electronic apparatusand will giveai'widerangelof capacity anmtnrciilxigw v t Other objectswill appear from time to time 1n the course ofthe specitltationlandclaims.

The. invention is, illustrated more or. less. diagrammatically i'n theaccompanying drawings. wherein:

Figure lii's aipfanview;

Figure; 2 is a section along` the line 2.--2 ot Figure'l;

v li'igure.y 3-is a lsection along, the line 3f-3-.of Figure l; and

Figure 4 is a partrplianl View of a modication of the condenser platesshown:k in Figure 1..

Iiuike. partsV are indicated by. like characters throughout thespeciiication and, drawings.

I is a chassis `base for a radio set. Punched out of a plane portion ofthis chassis is a relatively long rectangular aperture 2, bounded onboth sides by track members 3, which form guide slots to receive amovable condenser plate 4. There is electric contact between condenserplate 4, track members 3 and -chassis I. The movable condenser plate hasdisposed therein two rectangular apertures 5. Downwardly extending fromone end of the movable condenser plate is a nut 6, adapted to travelalong screw 1 The screw 'I is on a shaft -8 having a collar 9 enclosedin the socket IU, xed in position in the chassis. II is a tuning knob ofthe usual type fixed on the shaft 8 by the set screw I2. Rotation of thetuning knob II longitudinally displaces the movable condenser plate l.

Extending across the aperture 2 are bridge bars I3. Each bridge supportsby suitable means, such as screws I4, a xed condenser plate I5, which iselectrically insulated from the remainder of the apparatus. In a typicalconstruction the condenser plate I is electrically connected, byconductor It from the lug I'I, with the grid of 3 Claims.. (Cl.L15-41.5).

a tube preferably located immediately above the condenser. The lug Ii'ton. thel condenser plate: I5 is also.- connected by.- coill |18y togrounda lugt!!` on the chassis. Each bridge insulates the olv denser itsupports and is mounted on. chassis I by screw 20,. one end. ot which.holds the bar against a spacer 2t. Theother end` of the' bar rests on aleaf. spring 22 or other suitable flexible compressible support member,xbei-ng heid1there1 against by a trimmer screw 23. AAd/iustment. ci the`condenser is made by the spacer 2I and the trimmer. screw Z3Y andispring, 22. Interchange-r able spacers may provide coarse adjustment,spacers. of, different thickness being selected to give an appropriate:air gap to-v provid-e.r the capacity desired. which. willv depend on theusage,t thenv thelne adjustment ismade by turning the trimmer screw withav screw driver` in the-usual; manner. The adjustments are in the orderof thousandths. of an inch. and theexibility of theA bridge bar permitsadjustment, as the fixed' and movable. conductor plates-v are movedtoward or. tromv oneanother. The very slight angularity introducedV byadjustment of the. trimmer screwisso sllehtastobe negligible.

As the tuning knob is'rotated. the movable con-V denser plates move.back and forth increasing or decreasing the opposedv area. between.fixed andmovable plates, thereby changing the capacity oi the condenser.inthe wellknown. manner.

Because the movable. condenser plate: is aatl rigid structure moving.back and. forthA between guidesgwhi'ch adequately support both edges,and because it is displaced by the screw and nut drive mechanism,maximum accuracy results. No distortion, no twisting, no bending of theparts as is characteristic of a rotary variable condenser is possible.Change in the air gap is easily made so one condenser may be employedfor a multiplicity of uses, a large number of condenser plates may bestamped out in advance and assembled and adjusted easily. If desired, aseries of movable plates, or a series of fixed plates, may be used inthe same chassis for testing and the like to meet dilerentcircumstances.

While in Figure 1, I have shown the opening in the movable condenserplate and the xed condenser plate rectangular, I have illustrated inFigure 4 a situation where the plates are irregular because my inventionmakes it possible to design a structure wherein the parts of thecondenser may be shaped to give any desired tuning or any sort oftracking desired. Aside from this change in the shape of the twocondenser plates, the device of Figure 4 is the same as the device ofFigure 1.

The type of -condenser which I illustrate provides straight linecapacity tuning. The plates may be shaped to give straight linefrequency -or other desired characteristics. The trimmer arrangementallows slight adjustment in spacing between condenser plates withmicrometric precision so Vcapacitymay be changed to facilitate trackingand accurate tuning throughout the movement of the plate varies theareas wherein frequency band. The pitch of the screw and'- thread may beselected to give any desired displacement depending on the use, the typeof mechanism, etc. For FM 88-108 rnc., four turns for tuning the entirebandV has Vbeen found suitable.

An important advantage of my condenser is that by the use of the trimmerscrew or other suitable trimmer mechanism, whereby the gap between thexed and movable plate is micrometrically adjusted, I obtain accuratetuning through the entire frequency band for which the apparatus isdesigned since the change in capacity is symmetrical.

I have illustrated three condensers. However, the same principle'may beused for one, two or many more than three condensers as the case may be.I have illustrated an irregularly shaped xed plate. The irregularshaping might be applied to the movable plate or to both. I have shownair as the dielectric. -If greater capacity is desired, otherdielectrics might be used.

I claim:

l. A condenser including an apertured flat condenser plate, guide meanstherefor adapted to constrain it vto movement in a plane parallel withthe plate and means for moving it longitudinally in such plane along aline intersecting on the apertures therein, a plurality of separatecondenser plates insulated from the apertured plate, means forsupporting them in general parallelism with and adjacent but out ofcontact with the apertured'plate, said separate plates being spacedapart substantially equal to the spaces between the apertures wherebyeach condenser plate overlies one ofthe apertures and wherebylongitudinal movement of the plate varies the areas wherein theseparatev plates overlie the body of the apertured plate.

2. A condenser including an apertured flat condenser plate, guide meanstherefor adapted to constrain it to movement in a plane parallel withthe separate plates overlie the body of the apertured platemeans forsupporting the separate Yplates comprising bridges extending across thewith the plate and means for moving it longitudinally in such planealong a line intersecting on the apertures therein, a plurality ofseparate condenser plates insulated from the apertured plate, means forsupporting them in general parallelism with and adjacent but out ofcontact with the apertured plate, said separate platesbeing spaced apartsubstantially equal to the spaces between theV apertures whereby eachcondenser plate overlies one of the apertures and whereby longitudinalmovement of the plate varies the areas wherein the separate platesoverlie the body of the apertured plate, meansV for supporting theseparate plates comprising bridges extending across 'the aperturedplate, means for moving at least one endof each bridge toadjust thespace between the opposedv apertured and separate condenser'plates. 1

WILLARD M. TOWLE.

REFERENCES CITED Thefollowing reierenlces are of record in the fileof'this patent:

UNITED STATES PATENTS Number Name Date 1,580,621 Mahieu Apr. 13, 19261,623,360 Rodgers Apr. A5, 1927 FOREIGN PATENTS Number Country Date454,845 Great Britainv Oct. 5, 1936 591,082 France June 27,1925

